With a rapid increase of communication services, 3rd Generation Partnership Project (3GPP) licensed frequency spectrums become insufficient to provide higher network capacity. In order to further improve the utilization of frequency spectrum resources, 3GPP is discussing how to use unlicensed frequency spectrums such as 2.4 GHz and 5.8 GHz frequency bands. These unlicensed frequency spectrums are currently mainly used by Wireless-Fidelity (Wi-Fi), BLUETOOTH™, radar, medical, and other systems. Generally, access technologies designed for licensed frequency bands, such as Long Term Evolution (LTE), are not suitable for use in unlicensed frequency bands, because access technologies such as LTE have very high requirements for frequency spectrum efficiency and user experience optimization. However, carrier aggregation makes it possible to deploy LTE to unlicensed frequency bands. 3GPP proposes the concept of Licensed Assisted Access (LAA), which uses unlicensed frequency spectrums with the help of LTE licensed frequency spectrums.
Good orthogonality in LTE networks ensures a low interference level, thus there is no need to consider whether there are other base stations or other users around which are transmitting data, in uplink and downlink transmissions of a base station and a user. If LTE is used on an unlicensed frequency band without considering whether other devices are using the unlicensed frequency band, Wi-Fi device is subjected to great interference. As long as there is a service, the LTE will perform a service transmission. No monitoring rule exists. An idle state of a channel can be detected only after the service transmission of the LTE is completed. After that, the Wi-Fi device can perform a transmission.
Therefore, when LTE uses unlicensed frequency bands, one key point is to ensure that the LAA can coexist with the existing access technologies (such as Wi-Fi) on a fair-friendly basis. However, there is no listen before talk (LBT) mechanism to avoid collisions in traditional LTE systems. In order to better coexist with Wi-Fi, an LBT mechanism is needed for the LTE. In this way, if a channel is detected to be busy when the LTE uses the unlicensed frequency spectrum, the frequency band cannot be occupied. If the channel is detected to be idle when the LTE network uses the unlicensed frequency spectrum, the frequency band can be occupied. The prior art does not provide a scheme for performing uplink and downlink scheduling on an unlicensed carrier. Therefore, how to perform uplink and downlink scheduling on an unlicensed carrier is a hot research topic.